text:
Is training and pay different for cargo and airline pilots?
Do cargo pilots receive different training than airline pilots? Are there notable differences in salary or other benefits?
My assumption is that since cargo pilots do not have to deal with passengers, passenger emergencies, or bear the responsibility of passenger lives, they may have less training and/or earn less than their airline counterparts.

Passengers are simply self-loading cargo :)

@Jamiec self loaded??? Have you seen how much work it takes to get passengers to the right place at the right time and to sit in the correct seat?

Do cargo pilots receive different training than airline pilots?

First, cargo carriers are airlines just as passenger carriers are airlines, and cargo pilots are airline pilots. In the U.S. there is no difference in the training and certification of pilots dependent on whether they fly passengers or cargo. Also, be aware that airlines you generally think of as passenger carriers can also be operating freighters as well as carrying cargo on pax flights.
Whether there are passengers or cargo in the back, the airplane is having to operate in the same airspace, and a given aircraft model, whether in pax or cargo configuration, is essentially the same insofar as flying the aircraft. Indeed, at each of the two 747 carriers I flew for, we had both pax and all-cargo aircraft, and which we were flying made no difference in our pay rate. Pay rate is typically dependent on equipment flown, union contracts, and other considerations, but not on whether there are boxes or people in the back.
There are a few differences in flying pax versus flying cargo. Some that I can think of offhand are:

With pax and within 4000 feet of the ground we limited our bank to 20 degrees unless in cloud.
With pax we tried to avoid turbulence in general. With cargo not so much. Boxes don't complain.
With pax you are less likely to be concerned about weight and balance. Pax weight and balance is relatively simple, cargo weight and balance can be more of a problem.
With pax, you of course can have passenger problems, but those are almost always handled by the cabin crew. Only once did I feel that I really had to go back to the cabin, and that was because we had an inexperienced purser. Even then I could have sent the flight engineer or first officer, but I was bored.
With cargo, you don't have to worry about passenger announcements.
With cargo, you don't have to worry about dinging the flight attendants going through 10,000 feet.

Cargo is more fun, in my opinion, insofar as flying the airplane; you feel free to do things that you might not do with pax.
Pax is more fun on layovers, and you don't have to get your own meals, drinks, etc in flight, although I flew 3-man cockpits and the flight engineer often took care of getting those things on cargo flights.
Pax can be a problem on layovers where they're depending on the full crew being available the next day, because flight attendants increase the number of required crew members, and thus the greater the chance that somebody will get sick, get beat up, get in trouble with the law, get hit by a car, or run out of money and hit up the captain for an emergency loan. I had all of those happen .
Finally, arguably the life that the pilot is most interested in preserving is her/his own. Get yourself to the destination safely. What's in the back of the airplane will follow.

"Boxes don't complain", but the recipients might!

With pax we tried to avoid turbulence in general. With cargo not so much. I remember, more than once, hearing a phrase in the cockpit on cargo flights during turbulence. It was something like, "you gotta be tough to fly the mail." It was always stated in rhetorical tone as if it was a common axiom. Are you familiar with the phrase among cargo pilots?

@TomMcW I can't remember having heard that in relation to cargo pilots per se, but I seem to remember hearing it or something like it in relation to the air mail pilots of the 1920s. I think, though, that it was about the overall environment they had to operate in, not just turbulence.

@Terry That's the way they said it, like they were borrowing it from an earlier era. Like a tongue-in-cheek comparison to the harsh conditions of open cockpit airmail pilots. Must've been a FedEx thing :D

@TomMcW: Mail flights were the first scheduled flights, before there were regular passenger services. Mail pilots could not be picky about the weather, and that with wooden planes and open cockpits. It's definitely from the early Twenties. In Germany, an equivalent saying from that time was "only lunatics and Lufthansa will fly in this weather".

One addition: With cargo you have to deal with more dangerous goods and the associated paperwork and regulations, such as radioactive materials, lithium batteries, flammable chemicals, that are prohibited on passenger flights.

Doesn’t cargo only require a CPL, but passengers require ATP?

@bartonjs As far as I know, there is no distinction in U.S. regs insofar as pilot licensing depending on whether cargo or passengers are carried. However, I retired in 1999 and haven't kept up on the regs. I suggest you ask this as a question rather than a comment as there are those here who are able to quote chapter and verse. At the time of my retirement, you could fly cargo and pax with only a CPL under Part 135 (small aircraft), but an ATP was required under Part 121 and 125 (large aircraft) for both cargo and pax

At least in the US, "scheduled" flights are Part 121 and require an ATPL; non-scheduled flights are Part 135 or Part 91 and only require a CPL. Whether the cargo is self-loading or not doesn't matter.


text:
What do I need to power up an EDF engine?
I want to buy a EDF engine (just the engine). What items, such as battery and chargers etc. do i need to buy to power it up?

I'm voting to close this question as off-topic because specific purchasing advice is not within this site's scope. See the help center - "...it's not about…    Resource location: Where to buy a specific part"

but where do i find it then

Aside from being off-topic, the ancillary equipment you will have to buy will depend on the engine itself.

@Therac I think the main point of the question is to determine what is required, sources are just a bonus.

This has no connection at all to purchasing advice (which is like "should I buy a Ford or Chevy?")

Note that:   "Resource location: Where to buy a specific part" "  the question utterly does not ask "where" to "buy" a "specific" "part".  If the supposed reason for closure is "Resource location: Where to buy a specific part" " that is bizarre.

An EDF is an electric ducted fan, so I assume you're not interested in the fans powered by internal combustion engines (or actual turbines).
You'll need:

an ESC (electronic speed controller) that is rated for at least the maximum current and voltage of the motor in the EDF.
a battery that can provide that current and voltage.
something to provide a throttle signal to the ESC. Usually this is a transmitter and receiver, but for bench-testing a simple, cheap option is a servo tester.
a charger for the battery. This must be able to match the battery chemistry, voltage and capacity (they normally handle a range)
if the charger isn't mains powered, it will need a power supply.

There are loads of on-line shops for all this.

Great answer to a great question.

Yeah the Q&A really belongs on an RC forum, but great answer nonetheless.

source: Stack Exchange

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sort: votes


text:
Can I log flight time in unregistered helicopters?
Is there a way to log my flight hours from these flights?
During a time I was in middle east I had an opportunity to fly Astar for more than 200+ hours with multi experience majors as Long line, Rabbling, Mountain Operation, NVG, ... etc, however I'm not a licenced pilot but I have a good experience on Astar,
Now I decided to get use of that experience and put all the effort into some licenced actions but I have a hard time to find how to count my flight hours or if anything can be done with those hours.
I will appreciate all your help.
Cheers
Bravo

It would help if you were specific about what country you are attempting to get your license in, and what license specifically you are wanting to acquire.

It may help though to note that many ICAO compliant countries, unless you are under instruction of a flight instructor or you are a licensed pilot, you cannot log time towards a license or rating.

Even if you can't log the hours, you still have the experience that should make formal training a lot easier/quicker/cheaper -- assuming you don't have any bad habits to fix.

You may edit the question so that it is clear what you are asking for without the need to read the entire question. When reading the title, it should be obvious what you are asking for about flight time on unregister helicopter. Moreover, you should be more direct when you ask your question (e.g. "I'm an experience pilot and i want to know...." and then your story "i spend time in middle east..." )

I'm confused. You title says "unregistered helicopter" which indicates to me that it wasn't registered with the appropriate authorities in the country you were flying in, then your question says that you are not a licensed pilot. Are both of these statements true? I'm not sure if flying an unregistered aircraft has any impact on your ability to log time, but that might be an important bit of information to clarify.

If you're in the US, this question might be helpful. It would be good to know which country you want to train in but the comments by others are almost certainly correct: if you didn't fly with a certified instructor who signed your logbook for the flights, then they can't be used towards a license.

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text:
How to trim in level flight when speed increases?
What is required to happen to control surfaces and trim tabs to remain trimmed in straight and level flight, as speed increases? (for a GA propelled aircraft)
My manual tells me that the elevator should be further deflected downwards, and its trim tab further upwards.
I understand the reason for the trim to deflect in the opposite direction of the elevator (to help maintain it in that position), but don't get it for the elevator.

related: https://aviation.stackexchange.com/questions/2980/ (see the answers)

Thanks Frederico, but I don't see an answer to the above specific question in the post your are referring to. Why a downwards deflection (as opposed to upwards) on the elevator?

Oh, I know it does not directly answer your question, that's why I only said "related" and I have not voted this to be a duplicate. Sorry for the misunderstanding.

I know in my airplane, it is always wanting to climb!  Go faster, it wants to climb. Make a turn, it wants to climb. Get hit with strong, gusty winds, it wants to climb!  I have a stabilator, not an elevator, so the whole surface moves vs the front half (can't even think what that is called now!) being fixed and only the rear half being the elevator.

@CrossRoads: It's called a stabiliser.

Thanks, was drawing a blank on that.
http://www.americanflyers.net/aviationlibrary/pilots_handbook/images/chapter_1_img_32.jpg

The angle of attack is lower for the faster flying aircraft. More speed means more dynamic pressure, and in order to create the same lift (weight did not change, after all), less angle of attack is needed to create the needed amount of lift.
Now it is important to know that the angle of attack (more precisely, the difference between the actual and the zero-lift angle of attack) on the wing is higher than on the tail if the aircraft is statically stable. If the aircraft accelerates, the relative amount of lift loss on the wing is less than on the tail, because both experience the same reduction in angle of attack. To keep the balance between both the same, this extra lift loss on the tail needs to be compensated by some downward elevator deflection. The center of gravity did not change, and the center of lift must be shifted to the same longitudinal station in order to maintain level flight.
Fun fact: When transitioning from sub- to supersonic speed, the elevator must be trimmed trailing-edge-up, because now the center of pressure moves back on both wing and tail, so their lever arms around the center of gravity change.

As speed increases, the horizontal stab generates more lift... downwards. This would then force the tail down and the nose up, the wing would be at a higher AoA, and create more drag, and the aircraft would return to its trimmed-out speed. If you want to fly faster, you have to hold the nose down against the wanting-to-go-up tenfency, and thus you need down-elevator. And to hold this you then need forward-trim.

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text:
Why doesn't flightradar show many flights going over China?
I use FlightRadar to track some flights. I am surprised to see that there are very few or no flights at all going to air fields of china.
Is my observation correct? I really doubt that this is correct.
If its true what is the reason behind that?

Where does FR24 get its information from? Is that information available in China?

related: https://aviation.stackexchange.com/questions/30848/why-dont-aircraft-fly-over-tibet (possible duplicate)

Related

From the Flighradar How it works page:

Flightradar24 relies on volunteers around the world for the majority
  of our coverage

Note it implies:

There are people willing to contribute
These people can afford to buy receptors, gather the data and upload it to Flightradar

About point 1. In case of China how much people are willing to contribute? How many are affraid to do it to a foreign organization and how much are affraid of gettign the wrong attention from government?
About point 2. Most people on China cannot afford to buy such equipment (compared to USA).
It's easy to check point 2 by comparing macro economic statistics (So I doubt I need to link it here).
Point 1 is very speculative so each one should try to figure that by him/herself.
In fact I always wondered Fligth radar will got a poor coverage in third world countries (point 1) while getting near 100% coverage in USA.
Note also the size of aviation community (pilots, enthusiasts, aviation industry workers, etc) in USA is so much bigger tha in other corners of the world.
Edit's in response to Jaydeep comments
Flighradar giving away equipment like that is great, I think Wow!
Note also the note on the same page:

Exceptions to these requirements can be made to applications from
  unique locations.

So that begs the question if they are actually granting such gifts to China. For the sake of the completion I will ask them.
EDIT     and The Answer is:
So I asked Flightradar about it and they sent me the response below:

Hello Jean,
Thank you for contacting Flightradar24.com.
Your Support reference is 219752.
Yes, that is correct. We provide this free equipment to anyone in the
  world who has a good location with steady internet and power. The
  reason why you don't see many aircraft in the middle and west of China
  is because of the lack of receivers in these area.
You make an application and we go from there if it's a good location.
  If we already have receivers in the area then we put the application
  on hold but if its a good location then we provide them with a free
  kit.
https://www.flightradar24.com/apply-for-receiver
  -- Best Regards, Muazzam  Flightradar24

Straight from the horse's mouth the answer is simple "lack of receivers" what causes that is open to speculation but a quick search for "rural china power grid" and "rural china internet coverage" points out "steady internet and power" can be the problem.

Thanks jean for explanation.  regarding point 2, I think people dont need to buy receptors because they give it out for free. https://www.flightradar24.com/apply-for-receiver

Also regarding third world countries, India is counted as one, but we have superb coverage here.

@Jaydeep Another factor is possibly language barrier. India's been under british rule, so english is fairly prevalent. I believe english is far less prevalent in China. And I don't think FR24 is available in chinese. So probably fewer people in China even know about the free receiver?

Your observation is somewhat correct. Plenty of flights land at hundreds of Chinese airports every day. The main reason why it always seems so empty on FR24 (technological issues aside addressed by Jean), is that 80% of China's airspace is open only to the military. Civillian flights are restricted to narrow corridors, adding many miles onto a flight, while that big space in the middle of the country remains out of bounds. There have been talks about opening more of the airspace up, but for now it's a hell of a place to go flying.

Yes This helped me a lot to understand this behaviour, accor. to this article http://www.bbc.com/capital/story/20160420-this-is-why-chinas-airports-are-a-nightmare only 30% of airspace is open for commercial flights.

Flightradar24 gets all this data from thousands of ADS-B receivers that they have all over the world. Rural areas in China (Middle and western parts) don't have these receivers and hence not much data is shown there.
The kit they provide is free or charge and all they require from the recipient is to have a stable internet connection and power.
Application for these kits can be made here www.flightradar24.com/apply-for-receiver


text:
Is trimming for constant speed equal to trimming for constant angle of attack?
My understanding of trim:
When you say you have trimmed an aircraft for a constant speed, say 100 mph, you are actually trimming the horizontal stabilizer so that there are no forces on stick (or tail down force is balanced with nose weight) at that speed. To do that you either control the horizontal stabilizer/trim tabs until no force is felt on the stick.
My question is, (if my understanding is right), can I say that we are trimming for constant angle of attack instead of speed (and the constant angle of attack is represented in form of speed). By trimming the aircraft, aren't we making the aircraft fly  at constant angle of attack?
If so, can I make these following statements about trim: (ignoring the things like propeller blast etc..,)

When you are cruising in a trimmed condition and decrease( or increase) the engine power, the aircraft will pitch down (or up) until it finds the old angle of attack where all the forces are balanced and the trim is reestablished.
When you are cruising and closed (or opened) the throttle completely, the aircraft will descent (or climb) at the same trimmed angle of attack.

For a 1g situation I would generally agree that you are holding a constant angle of attack which is evidenced by a constant indicated airspeed.  However, for maneuvers with a grater than 1g this doesn't hold true.  We know the airplane stalls from exceeding the critical angle of attack and the airplane can stall at any pitch attitude and airspeed.

Related -- https://aviation.stackexchange.com/a/77249/34686 -- trimming for constant angle-of-attack is not exactly the same as trimming for constant speed, if we are including climbs and descents as well as level flight.  But it's a good first approximation to say that they are the same, if the climb or glide angle is not too extreme.

Short answer: Yes
Generally you are right. You are trimming the aircraft for a point on its polar, and that point is reached at a specific angle of attack.
You say yourself we should neglect secondary effects like the propeller blast, and under this condition you are right. Trimming means to set the distribution of lift between wing and tail surface, and this directly sets the angle of attack.
Now the more elaborate part of the answer
You trim the aircraft for a specific dynamic pressure, that is the product of air density and flight speed. If you slightly change your question from "trimming for constant speed" to "trimming for constant indicated speed", you gain precision and the answer is still yes. With a change in altitude you will also affect the Reynolds number the aircraft flies at, and the same polar point is reached at a slightly higher angle of attack the lower the Reynolds number gets when the aircraft climbs into colder air.
In turns the lift demand is increased. Not changing trim during a turn will let the aircraft speed up to increase lift at an unchanged angle of attack. That is why you pull more when turning - you want to increase the angle of attack, so speed can stay constant. When speeding up, you again change the Reynolds number and indirectly also the angle of attack, but this effect is very small.
When you change the power setting, you add energy to the aircraft at a different rate. Thrust becomes bigger and is counteracted by the sum of drag and the component of weight which acts in parallel to the thrust vector. Now the vertical component of weight is reduced, and so is your need for lift - but ever so slightly. This effect by itself means you will fly at a slightly smaller speed which will also very slightly affect the angle of attack. But since you did not change trim, the distribution of lift between wing and tail is unchanged, so the angle of attack is the same, save for a minuscule Reynolds number effect.
Increasing thrust will also increase the prop blast over the tail surfaces, making them more effective and slightly changing the balance of the aircraft. Depending on the direction of tail lift, the result is an increase or a decrease in angle of attack, but this is precisely the effect you wanted us to disregard.
Another secondary effect is a constant loss of weight as the engine burns fuel. This makes the aircraft lighter, so it requires less lift and a smaller angle of attack over time to remain at the same speed. Since you trimmed a specific polar point, the aircraft would need to slow down in order to stay at this polar point at its lower weight. But the lower weight also creates less drag, so instead of slowing down the aircraft will climb. Now the reduced density will require more angle of attack and will reduce engine output so in the end the same angle of attack is maintained at a higher altitude but a slightly lower indicated airspeed.

And the weight of the aircraft changes in time, so instantaneously the proposed equality holds, but in some time the aoa will decrease (due to consumed fuel). ;)

@GürkanÇetin: No, weight loss will reduce trim speed. AoA stays the same (again, save for small Reynolds number effects).

What I mean is if you keep constant airspeed (suppose no climb) aoa would decrease. (Would be noticeable for a slow flying aircraft). The question was trimming for speed, so I took this side. If u keep aoa, then speed would decrease, you're right.

@GürkanÇetin In order to keep constant speed with reduced weight you need to re-trim the aircraft. This must be commanded by the pilot. If the pilot sets trim once and then flies horizontally for a while, speed goes down with the square root of the weight loss. It's the inverse case to the speed increase in a turn.

Gotcha!  I see what the source of my confusion was.  Descent doesn't mean that net lift and weight aren't still equal when there is a 0 net acceleration.  Answer removed.  Thanks for clarification.

@GürkanÇetin: I expanded the answer, and the aircraft will climb. In order to remain at the same angle of attack and altitude, power needs to be adjusted.

In a jet aircraft, where the fuel weight can be 30% to 50% of MTOW, the 'secondary effect' of weight loss through fuel burn is not small at all.

Excellent question. Yes, when you trim - you trim for angle of attack, all other factors notwithstanding (i.e., aircraft configuration, location of Center of Gravity, etc.) The fact that trimming an aircraft will hold the same speed with changing power settings is an ancillary consequence of trim in so far as level flight is concerned.
This trimming for angle of attack also holds true for an aircraft within a banking turn. Because of the greater wing loading within the turn, itself, the natural trim of the aircraft will actually seek a higher airspeed to maintain equilibrium at that same angle of attack. If power is not increased, the airplane will descend in search of this equilibrium. However, if power is added, and the airplane is banked to check its ascent, it will continue to hold the same angle of attack but at the higher airspeed.
Incidentally, I've been told this is why the Navy initially started for fly constant angle of attack approaches as opposed to constant airspeed...even before the advent of AOA Indicators and Approach Indexers in the late 1950's.
Back then, they were flying basically a flat approach from the 180 position into "the groove" just astern the ship, dropping to 90 feet above the surface to give themselves just over 20 feet of clearance at the Fantail, not accounting for any pitch and heave introduced by a ship steaming into the swells, before an LSO issued a "cut-signal" whereupon the pilot would chop power, hold the nose, and plop down onto the deck. But this precariously low altitude became outright dangerous in the jet age with approach speeds of 120 knots. To forestall the specter of flying into the waves approach procedures were codified to insist that, by the time a pilot reached the 180 position, they be configured (hook, wheels, flaps - down), and trimmed-out "on-speed" before commencing their turn into the ship's wake. Once done, power was to be added to maintain altitude within the turn but NO PITCH COMMANDS WERE TO BE INTRODUCED! They were to accept whatever speed this trimmed condition demanded. Starting at 120 knots, and using a quarter-banking turn (22.5 degrees), this resulted in an airspeed increase of around 5 knots. Apparently, it worked and has been gospel since.
Whether this story is apocryphal or not is a matter of debate - I got it from a retired Navy Commander whose career spanned from the late 1940's into the 1970's; from flying props to flying F-8 Crusader's. I've never been able to find any published documentation to support this, but it seems plausible enough to share it with you here today.

Re your discussion of what happens when the aircraft is banked-- that's a good description to a first approximation, but there's an additional complication, especially in slower-flying aircraft.  For more, see https://aviation.stackexchange.com/a/76823/34686 -- the relevant part starts about halfway through the answer, in the paragraph beginning w/ the sentence  "But what if we are not beginning the maneuver at a high "angle-of-attack of the fuselage", and/or we are rolling slowly enough that the above dynamic is trivial?"

Possible suggestion--there may be some room to clarify-- "Once done, power was to be added to maintain altitude within the turn but NO PITCH COMMANDS WERE TO BE INTRODUCED! They were to accept whatever speed this trimmed condition demanded" -- readers may wonder whether you really meant to say that the aircraft's pitch attitude was not to be changed, which is rather different from just letting the aircraft fly at trim, pitch-wise, as power is added to stabilize the altitude.  Either way, the pilot would want to start by trimming the aircraft, but the end result would be slightly different.

But if you meant it just as you wrote it, then no need to change anything--

This is an interesting question. I believe that both of your statements are wrong though.
"Trimming for constant speed" is technically not possible, as the trim itself has nothing to do with the speed. As you probably know, you have to adjust both throttle and trim to have the plane fly level at a constant speed. Trim only controls your elevator (neglecting the other two trims that larger aircraft usually have as well). When you "trim for constant speed", you usually adjust your power setting while keeping the plane flying at a certain altitude. Then (or even while you adjust your speed) you trim the plane to take work of your arms ;)
Once you're flying at a constant speed, you can say that the angle of attack remains the same when you're not descending/ascending. No comes the tricky part though:

You're saying that the aircraft will find a balanced condition again - which is right. Yet you have decreased the power, thus you've changed one force. Because of that, the other forces must change as well to balance each other out. The angle of attack will thus NOT be the same when the throttle is different.
Again, when closing the throttle, the aircraft will find a new balanced condition, and again, the angle of attack will change.

Another interesting question is: When you are flying at a trimmed condition and decrease the throttle, then after a while increase it back to the original setting, will the aircraft return to level flight? - The answer is yes, but no ;) Yes, because now all forces are back to the original condition, thus the airplane must have the same attitude. No, because by descending, the air density will change, thus resistance of the air becomes bigger which enforces a bigger force or resistance on the plane messing up the balance again.

I believe "you have to adjust both throttle and trim to have the plane fly level at a constant speed" should really be "at a given speed". You can do a levelled fly at any reasonable power setting, and the speed will be constant (in time). I just think this can be a source of confusion.

One important point is that you have decided to constrain your answer to level flight, which changes a lot (especially since the OP even refers to pitch and altitude changes in his question). Because of this, your answer doesn't really accurately answer the question.


text:
What is the effect of airfoil thickness on aerodynamic lift?
More than once I`ve read that the airfoil thickness contributes little to the lift compared to the angle of attack and airfoil curvature and has more to do with airfoil stall characteristics.
Could anyone explain this, preferably mathematically?
Thank you

http://physics.stackexchange.com/q/71681/2498 http://physics.stackexchange.com/q/259113/2498 and http://physics.stackexchange.com/a/276266/2498 will help you here.

In chapter 2 of his book Fluid Dynamic Lift, Sighard Hoerner discusses the influence of thickness by going to the extreme of an airfoil with a circular cross section:

Assuming that we would manage by means of boundary layer control
  around the rear side, to displace the stagnation points from zero (at
  the forward side) and from 180° (at the rear side) both down toward 90°
  (at the lowest point), without losing any momentum, its lift curve
  slope would be dCL/dα =4π, rather than = 2π, as in thin foil sections.

Since you desire a mathematical expression: This is the linear approximation he gives:
$$c_{L\alpha} \approx 0.11 + 0.09\cdot\frac{t}{c}$$
Note that the lift curve slope is per degree. $\frac{t}{c}$ is the relative thickness of the airfoil.
In figure 21 of that chapter he uses the concept of the lift angle, the angle at which the lift coefficient reaches unity, to show how the lift curve slope varies over airfoil thickness. This plot should demonstrate how limited the applicability of the approximation is in reality.

The lift angle of airfoil sections as a function of their thickness ratio (picture source).
Stall is dominated by flow separation, and the displacement effect of an airfoil adds to the stresses on the boundary layer which determine when the flow separates. On the other hand, thickness is indirectly influenced by the nose radius of the airfoil, and this in turn determines the suction peak at the nose and at higher angles of attack. A higher suction peak also stresses the boundary layer. In consequence, both a too small nose radius (and too small airfoil thickness) and a too high thickness lower the maximum lift coefficient. The sweet spot is at a thickness of around 10%.
In chapter 4, Hoerner looks into that dependency in detail. The plot below does not include highly cambered, thin airfoils, and the straight limit for thin airfoils is misleading.

Maximum lift coefficient of various types of airfoils as a function of their thickness ratio (picture source).


text:
What's the meaning of underlined frequency in sectional chart nav aid box?
There is a statement to describe the underlined frequency in legend, it says:

Underline indicates no voice on this frequency.

What does this mean? We still need to ident the Morse code, doesn't it? So what's the "no voice" referring to?

Navigation receivers can be used as a fall back for regular VHF/HF radio transceivers
Before data links, there were essentially two types of radio receivers in the flight deck, and this is still the case for most GA aircraft: "COM" used for voice communication, and "NAV" used to receive navigation signals. When COM transceivers fail, the pilot is left without information from ATC, and will follow their current flight plan and clearances.
However ATC may try to send additional information and new clearances using the NAV radios. In that case this is a one way communication, as NAV aboard the aircraft have no transmitting capability.
Information provided to ATCO by FAA in JO 7110.65:

a. In the event of lost communications with an aircraft under your
  control jurisdiction use all appropriate means available to
  reestablish communications with the aircraft. These may include, but
  not be limited to, emergency frequencies, NAVAIDs that are equipped
  with voice capability, FSS, Aeronautical Radio Incorporated (ARINC),
  etc.
  [...]
b. Broadcast clearances through any available means of communications
  including the voice feature of NAVAIDs.

The voice feature is present on all navaids, except TACAN. It may also be used to transmit ATIS when no communication emergencies are going on.
Pilot has also instruction to use NAV receivers, e.g. in AIM 6-4-1. Two-way Radio Communications Failure, 6-4-3. Reestablishing Radio Contact:

a. In addition to monitoring the NAVAID voice feature, the pilot
  should attempt to reestablish communications by [...]

Audio mixer, source
Navaids without voice capability
No voice or underlined frequency indicates ATC can't use this navaid for to transmit voice messages.
Such navaids have a class code W (without), e.g. CHANDLER NDB in Arizona:

Source: AirNav

Source: SkyVector
See also:

NORDO.

Why do you say The voice feature is present on all navaids, except TACAN. then you talk about Navaids without voice capability? So, not all Navaids have voice feature, right? BTW, the link to the AIM is broken, here is a good one https://www.faa.gov/air_traffic/publications/atpubs/aim_html/chap6_section_4.html

@rvernica: I believe I wanted to say all navaids are ready for voice transmission, but only some have a voice source connected to them (e.g. microphone). One key aspect is the design must allow the modulation index to stay within acceptable range (no over modulation) when navaid signal and voice are used at the same time. For example: In the ILS, the localizer signals are modulated at 2x 20% only, to allow 50% for voice, regardless the actual use of voice. For comparison, the glide path signal which is not used for voice is modulated at 2x 40%.


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What kind of g-forces do birds experience and how does it compare to humans?
So bit of an odd one, but I was just looking at a sea-gull flying and wondering what kind of G-forces it could see in day to day flight?
There are probably very fast birds of prey that when pulling out of dives must experience fairly high G Force, but can they (in general) handle more or less than a human flying an aircraft?

Fun fact: The fastest bird in the world, the Peregrine falcon (240 mph in a dive) has pop-up vortex generator feathers delay flow separation during a dive! (But no winglets @Peter Kämpf)

Birds regularly experience up 10-14 G according to this website. After looking at how birds and insects fly, scientists came up with the conclusion as to how birds cope with this is because:

Animals will always have some advantages over machines, such as the ability to use their nervous systems to sense subtleties about the environment around them and alter their flight accordingly.

further up near the top, it mentions comparisons between birds and high performance military aircraft, such as this:

A Blackbird jet flying nearly 2,000 mph covers 32 of its own body lengths per second. But a common pigeon covers 75 of its body lengths a second.
  The roll rate of the aerobatic A-4 Skyhawk plane is about 720 degrees per second. The roll rate of a barn swallow is more than 5,000 degrees per second.
  Some military aircraft can withstand gravitational forces of 8-10 G (Earth's gravity is equal to 1 G). Many birds routinely experience G-forces greater than 10 G and up to 14 G.

According to another website the reason humans can't cope with high g's as well is because:

Every bit of our muscular-skeletal system is naturally crafted to deal with Earth’s gravity. Were you to travel to a planet that had a more significant gravity, a more massive planet with 5 G’s for example, you would either be unable to lift yourself off the ground, our the new weight-force would be so much that the air would be forced out of your lungs and your eyes would explode (something gruesome for sure).

crazy stats about the pigeon covering it's own body twice as fast as an SR-71! and the 5000degs/sec roll rate. thanks for the informative answer!

How long does it take for a bird to pull out of a dive?  The bird's body might change orientation in less than 0.1 seconds, but that doesn't imply that the first's downward momentum won't continue for some time after that.

That claim about 5Gs causing human eyes to explode etc. sounds suspiciously like bunk. John Stapp is probably grimacing in his grave.

Fighter pilots routinely experience 5 Gs without any exploding of eyeballs. But they only experience it for relatively short periods of time. Living on a 5 G would is almost certainly possible, but it would present great physical challenges, at least for a while and possibly for life in some ways. One would eventually build up the muscles that would help deal with the increased gravity, and one would probably do little but sleep and eat and walk around briefly for the first several months at least. But I doubt it would be short-term fatal, although it might shorten lifespan.

@ToddWilcox: In a 5g world otherwise comparable to Earth, atmospheric pressure would by multiplied by 5 (weight of air column) and heart would have to pump blood 5 times heavier to brain, this means at least more muscle power available from respiratory and blood systems, so completely different diet. The heart could be too low relatively to the brain for brain to receive blood as required.


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How much power do planes use when taking off at London City?
I watched a video of an A318 taking off at London City and it took just 20 seconds from setting takeoff thrust to getting airborne.
BA A318 takeoff @ LCY (takeoff thrust @ 1:23, airborne @ 1:43)
and here's A319 takeoff in a regular 3.5km runway, taking ~38 seconds
S7 A319 takeoff @ OVB (takeoff thrust @ ~3:26, airborne @ 4:04)
What I'm asking is a thought experiment, let's say, we fly from one airport to another, and everything is the same except runway length. In one case it's 1500 m, in another it's 3500 m.
How much thrust does an A318 (or any other aircraft certified to fly at LCY) apply at a regular airport vs on a short runway like LCY? How much thrust is used (in kN) and what is the thrust/weight ratio?

Related: you may refer to here where I did a calculation about the thrust (and energy) to get a 747 airborne.

This isn't a simple answer. It depends on the aircraft loading, engine configuration, air temperature, runway length, safety margin, etc. There isn't a set number for an A319 or A320 for example. The FMS calculates takeoff thrust when the pilots input various parameters.

@RonBeyer I understand. I'm not asking about something very precise, but rather a comparison, what if everything else is the same, except runway length.

Takeoff thrust is calculated by a computer (or by looking up tables), since a lot of factors are considered:

Takeoff weight
Effective runway length
Runway surface condition (dry / wet)
Air temperature

"Effective runway length" is calculated from runway length, wind direction, wind speed, and runway slope.
Since we do not know the takeoff weight of the specific flights, I will make an assumption here and set it to 80,000 KG, which is the highest figure I have in the reference table.

At a temperature of 20 degrees Celsius, takeoff weight of 80 tons, effective runway length of 3000 meters, the speeds from the table are: V1 at 145, Vr at 153 and V2 at 155. This is the takeoff with max thrust, which according to Wikipedia, each engine is delivering 120 kN of thrust. The thrust to weight ratio would be 0.15. Converting the variables to SI units, I calculated that the time to reach V1 to be exactly 10 seconds.
This calculation is, obviously, far from reality, as it assumed:

Thrust application is instantaneous.
The aircraft maintained a constant 1.5 ms-2 acceleration. In reality, aerodynamic drag will come into play as the aircraft picks up speed.
Max thrust is used on takeoff, which is rare in operations.

Moving on to shorter runways, the shortest runway length in the table I have is 2250 meters. It states that at this length, the maximum takeoff weight is 74.2 tons, and the limitations which resulted in this figure is runway length and Vmu(Minimum Unstick speed), the lowest speed at and above which the aircraft can safely lift off the ground with sufficient control surface authority and without a tail strike.
From the few data points I have, it seems that on a 1500 meters runway, the maximum takeoff weight would be around 63~65 tons.

So to answer your question:

If they used the same thrust, then the takeoff weight on the short runway is around 78% of that on the long runway.
If they kept the same weight, that would mean the pilots have extra thrust at their disposal on a longer runway. They can choose a derated takeoff thrust from the options -4%, -8%, -12%, -16%, -20% and -24%.

Source: A318/A319/A320/A321 Performance Training Manual

The question is asking about takeoff power levels, and your answer seems to be mostly about weights and speeds. I know they're related, but you don't seem to really address different thrust levels until the very end here, and only briefly.


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Why is there a hole in one of the layer of an airplane's windows?
On a commercial airliner, there is a hole in one of the layer of the passenger windows.
See here:

and here:

Or in more detail:

Can you explain the physical reasons for this design choice?

Not exactly a dupe, but the question is adressed here: http://aviation.stackexchange.com/q/673/95

@yankeekilo Well spotted. The title and slightly different subject of the other question made me not find it when searching before asking. Since there is not a lot of details in the answer that address it http://aviation.stackexchange.com/a/681/1599 I suggest we keep this one open.

I agree with @Guillaume

Aircraft windows are multiple layers thick. The side facing the passengers is just a plastic sheet, since they wouldn't want the passengers scratching up the actual expensive glass window. Beyond the inner pane there are two actual structural window panes. The outer one is normally the one bearing the load, while the inner one serves as a backup.
However, since pressure changes in the cabin during the flight, it's also necessary to equalize the pressure between the window panes, and hence the little hole. A hole of that size would not jeopardize pressurization even if the outer pane blew out. Note the label "Breather Hole" in the diagram below.

There is a rubber seal around the outside of the two panes so it would be a bit of a pain to open a hole to cavity from the side. Apart from that, the windows are pretty tight together and by keeping it where it is there is nothing in the vicinity such as dust that could gradually be pulled in.
Since the air in between the panes is colder, it's not unusual to see ice crystals forming around the hole as the more humid cabin air enters the cavity.

(source: gentex.com)
787 Window
This diagram includes the electric shade system of the 787 which is fairly similar. Since the two outermost panes carry no structural purpose you can just have them equalize air as you please.

So on the 787, where the hole would be? On the interior window pane?

I'm not sure how the 787 is, but here's a picture: http://www.airlinereporter.com/wp-content/uploads/2012/11/787-wing.jpg and it looks like it might have two holes, but i'm not sure where these are located. i'm not sure if you can just drill through these electrochromic panels, or if there might be a bypass on the side to fulfill the same purpose...

I'm still confused by the need of the 2 panes if an hole in the interior pane make the pressure adjust to the cabin.

There's a seal on every window and therefore every pressure until the final 'real' window has to be equalized since otherwise these would blow or crack. does this answer your question? :)

No, sorry, still a bit curious! Totally agree on the seal on every part until the last (outer) window pane for pressure equalisation. But I'm now wondering why the Structural Cabin Window System would have more than one pane? Is it to control the pressure change rate in case of damage on the outer pane as hinted here http://aviation.stackexchange.com/a/681/1599 ?

I'm pretty sure this is for safety/redundancy purposes. Both are designed to be strong enough for the pressure difference, but in case there's a structural defect in one, it will not lead to the complete blowout and loss of cabin pressure. I'm very sure the cockpit windows are double paned as well for the same reason. Looking on a few forums, it seems to be that the outer panel is designed to carry the load, since there's a very small bleed between the inner window and cabin air to equalize the space inbetween.

Wouldn't another key purpose of the glass layering be to limit heat loss?

I've borrowed some of your images here.


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Is it possible to get permission to fly a quadcopter around the St. Louis Arch for non-professional means
Is it permissible to fly a small quadcopter (<1 kg) around St Louis Arch for non-commercial means? If so what permit/permission is required?

I’ve edited your question based on the assumption that it’s a small personal use drone, as the total mass is what matters, not the battery spec.

The Superintendent's Compendium for Gateway Arch National Park says

Launching,  landing,  or  operating an  unmanned  aircraft  (UA)  from  or  on lands  and waters administered  by  the  National  Park  Service  within the  boundaries  of  the Jefferson National Expansion Memorial  is  prohibited  except  as  approved in  writing by  the  superintendent.

Since drone flight is not listed under activities that require a permit they clearly don't approve such activity on a regular basis. The only way I imagine they would approve non-commercial activity is if there was some sort of organized event. On an individual basis I expect the answer would be no.


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Can a helicopter fly VFR at night in India?
As per the title, can a helicopter fly VFR at night in India?.
If yes, can the pilot ask for special VFR?

I  know in the Netherlands (and that would mean the rest of EASA territory) you'd need an additional certification on top of your PPL to be allowed to do night VFR, irrespective of aircraft type. You should check that with your license authorities as well.

So what I understood from your answer is that helicopter can fly VFR as icao guidelines, just we have to check for any certification from licence authority Thank you

In short, yes, a helicopter can fly at night, in the US.  Special VFR requires that the aircraft and pilot be instrument capable, but that requirement is not applicable to helicopters.  VFR weather minima are different for helicopters than airplanes.

Sir please give references with respect to ICAO documents.

I am so sorry.  I answered for the US, not knowing that your question domain was India.  I am not familiar with India's regulations.  ICAO Annex 2, 3.6.2.4(c), chap 4 covers VFR, in general. Table 3-1 has helicopter weather minima.

Thanks for reference


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Is screen burn-in a problem?
Screen burn-in can be a problem for older and cheaper monitors.  It can be caused by fixed-width text, fixed-size graphics, and operating for long durations, which are things that are common in aircraft displays.
So is burn-in a problem for aircraft? Have there been hardware or software improvements to minimize burn-in?

Personally I've never seen a screen burnt on a modern monitor (e.g. post 1985), and "protections" like screen savers have never been required for CRT. Old CRT, with old phosphor (e.g. on oscilloscopes at slow scan speed) were problematic. Tube manufacturers were only a handful, and all competing for the best quality.

@mins, I've seen plenty of burnt-in later-generation (1990s) CRT computer monitors. Generally it was noticeable only on a switched off screen, but then rather clearly. I've also seen a badly burnt-in LCD monitor, but that one was on for weeks if not months, displaying the same white-on-black text.

Burn in is a problem with current OLED displays, which are primarily used in phones

@Zeus not seen any burnt in screens in a long time though, last probably was in the early 2000s working in a software testing lab where the same screens were often on for weeks or months on end showing the same information, mimicking the production environment those systems would be used in.

I was in the Regional Jet industry a long time and never heard of screen burn-in as a complaint on Rockwell Collins ProLine CRTs.  You mentioned "cheaper" monitors and that may be the key.  CRTs built to an aviation TSO (Technical Standards Order) are by no means cheap.

One would also hope that the screens are easily replaceable, too.


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Why didn't Philippine Airlines Flight 113 dump fuel prior to forced landing?
Philippine Airlines Flight 113 operated by a Boeing 777 bound for Manila suffered a compressor stall and engine fire.
I wonder why the pilot didn't dump fuel from the left-side prior to the landing to meet the maximum landing mass (MLM) required and to avoid damaging the undercarriage as seen in pictures?
I assume that, when I have an engine fire, I shut it down and crank the remaining fuel residual until it is put out. Any idea?

For reference, the incident is https://avherald.com/h?article=4cf94f2d&opt=0. No mention of landing gear damage.

… note that deflated tires and burnt brake pads, which are common consequence of brake overheat, the main issue in overweight landings, are no big deal, because these things don't last that long in regular operation either.

@JanHudec: that sounds like a good answer: it didn't damage anything serious or expensive, and probably the pilots anticipated that.  So the cost downside to an overweight landing is low.  That's a nice complement to John K's answer about the possible safety upside.

Also covered by the  blancolirio channel.

Dumping all the fuel on the left side would cause catastrophic imbalance leading to loss of control and a crash.  It would likely lead to a crash much faster than "simply" having an engine on fire.

I have to disagree Freeman, jettison nozzles dumps only for 15 minutes and its purpose to reduce fuel volume not emptying the tank, plus you can always cross feed from the others tanks to regain the balance instantly as you are dumping for weight reduction yet you maintaining stable balance

If you had an engine fire, even though it may be "out", you want your airplane on the ground as soon as you possibly can.  You don't know what structural damage is lurking as a result of the fire.  Dumping fuel would take a fair amount time to get rid of any significant amount.
So it's "Screw the landing gear.  We're landing overweight".

I also wonder if dumping fuel while engine is on fire would not create a dramatic fire hazard.

@LéaGris it is actually allowed. The fuel jettison nozzles are located further outwards on the wing for exactly this reason.

@LéaGris Nah, mostly it just looks cool.

On twin-engined aircraft the standard procedure for engine failure is to land as soon as possible. Since it is possible to land overweight—and aircraft are designed so that it is—delay to dump fuel is not considered acceptable, and no reasonable pilot would delay the landing when they can land already.
Landing overweight is not really a big issue. The limiting factor for maximum landing weight is the kinetic energy of the aircraft that will be dissipated on the brakes as heat. If the aircraft is overweight on landing, the brakes will probably overheat. But:

Since they had engine fire, the fire engines were on stand-by anyway, they can deal with hot brakes too.
The heat often causes tires to deflate and the brake pads might be burned, but those need to be replaced quite often anyway, so it's not a big loss.
The aircraft can't depart again until the brakes cool down, but it's not flying anywhere until they replace the failed engine anyway.

So it's safer to just land overweight than spend longer in the air with only one engine.

The only real fallout, unless the crew lands hard and breaks things, is an overweight landing inspection, basically a visual inspection looking for deformed or cracked structure.

Basically this: Engine Fire > other problems from overweight landing.

It should be noted that all the tires deflated upon landing

@Machavity, all tires deflated, but most probably after landing. It is kind of expected result. The brakes heat up to white hot (900°C is quite expected) and that starts to heat the tires and the air within expands. There are fuse plugs that will melt and release the pressure before it could cause explosive decompression. By that time the aircraft has turned off the runway (if possible), is surrounded by firefighters, and if there was still active fire on landing, it is already evacuated.

If you are landing overweight and single engine, you are almost gauranteed to blow tire fuses because a lot of airliners (I think the 777 included) land with half flaps when single engine so the Vref is considerably higher.  More weight than normal, and more kinetic velocity to cope with as well.

The fire engines being on stand-by is surely a very minor consideration. Even if they weren't on stand-by because of the fire, the pilot can just tell the airport to have them ready.


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What's that in front of the overhead panel?

There is that thing I have see a few pilot using it. it can be pulled outside and then inside. what's that and what's the use of it?

It's where you stow the garage door remote ;)

Actually, it's where the bar is.

@GdD Wow, didn't know that! I thought if you pull it it activates the ejection seat.

That's where the analogue/backup compass is stowed. The compartment can be opened downward if you ever need to use the compass, as seen in this image:

Why is it designed to be stowable? It doesn't seem to impede cockpit visibility when deployed, and surely the stowing mechanism adds at least a little bit of weight and cost. Is it just for aesthetic reasons?

@David Just a guess, but I suspect that Airbus management was embarrassed to put such a low tech instrument into their most advanced cockpit. So they decided to hide it after pilots refused to fly without.

@PeterKämpf It likely would not have passed FAA certification without one, though. It's standard equipment required on any aircraft.

Being stow-able means less likelihood of accidental damage (which, as its probably on the MEL is quite significant), you can turn the light off unless its in its open position etc etc etc.

I believe the Airbus terminology for this guy is standby compass, but the description as a backup/analogue compass is accurate.

Would it be worth its own question to ask why such an instrument wasn't designed to be always visible and the expectation of comparing it with the digital system built into standard procedures?

@TheLuckless: likely because the main failure mode for a primary digital compass is display failure, not inaccuracy. It's a pretty simple system all things considered.


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What happens if a crew complies but does not read back ATC instructions?
For example, a commercial airliner is inbound and is in the traffic pattern; ATC instructs the aircraft to reduce speed to 160 knots, which the airliner does. ATC notice the aircraft has complied but never read back the instruction. Would the air traffic controller file some type of complaint against the crew?

Look up "Kennedy Steve" on youtube, there are plenty of examples of this exact thing.

@Jesse_b Steve's a ground controller.  OP is talking about tower ops, it sounds like.

@J... Air traffic controllers work all positions, usually all in the same day. Steve's funniest recordings just happen to be on ground, but I don't think the rules for disobeying ATC differ very much between positions.  There is still the same level of danger on the ground with planes crossing active runways, etc.  Also I believe Steve no longer works control at all but is now in a management position.

@Jesse_b I don't know, I get the sense that ground chatter is a bit less strict than other ATC; if not by the book, at least in practice.  I've never heard Steve working anything but ground, though, before he moved on.  You've got me curious.

What happens if you are on the phone with someone and they stop responding? Do you send them a complaint, or do you first ask them if they are still there and if they heard what you said?

@J...: Steve on tower and Interview with Kennedy Steve

@Jesse_b The reason Steve isn't controlling now is that he retired a couple of years ago.

@reirab: That interview video is from Dec 2018 and takes place in Steve's office in the Kennedy airport.

@J.Hougaard well considering communication is far more important than a phone call, I thought I’d ask if there would be consequences regardless of what pilots said in the end.

No, ATC would not file a complaint for a single missed read back. In order to file a complaint they'd need to have very good reason to believe that the pilots were willingly breaking communication regulations, and there are so many other valid reasons for why this scenario could happen:

The pilots may have responded but it may not have been received. If two stations talk at the same time the stronger one wins, so they may have read it back but it was lost
The pilots may be dealing with a problem, or have a high workload. Communication is the lowest priority, flying the airplane safely is first, then navigation
The pilots may have a technical problem with the radio
The frequency could be too busy to get a read back in, sometimes the frequency can be so dense with communications you can't get a word in edgewise, so the pilots may comply and eventually just give up

These are just a few reasons from my own personal experience when I haven't read back an instruction or my read back wasn't received. If ATC is worried about it they can always call me back.
EDIT: The readback is a requirement for some instructions and I am in no way saying it's okay not to. My answer is for the specific scenario given, I think that the FAA would and should bust people who fail to readback in certain circumstances.

+1   In my experience, if someone misses a read back, ATC explicitly ask them to read back the instructions.  If that doesn't happen they ask the pilot if they are still on frequency and if so, continue to badger them for a read back.

Yes that's because the clearance or instruction doesn't have "legal status" technically until the readback.  A friend was busted when he went through the altitude of the initial clearance because a new altitude was cleared and he just dialed it up and kept climbing and passed the original cleared alt before he read back the revised clearance.  At the time the ATC unit was having a difficult time with pilots over some incidents and was following a kind of zero tolerance policy as retaliation.

@DaveGremlin But why bother if you can see on the scope that the pilot has complied?  "Ukraine 478 turn right heading 090" (Ukraine turns right to 090) (silence) that's your readback

@Harper-ReinstateMonica presumably to avoid letting dangerous habits develop.  If they had misheard the instruction and did the wrong thing, instead of just reading back the wrong thing and getting a correction, that would be a lot worse.  I'm just guessing about this, but I assume that's (part of) the reason for the read-back rule in the first place.

"aviate, navigate, communicate"

@Harper-ReinstateMonica This must not happen!! ATCs principle is: “never base control on assumptions!”. That’s why you need a readback. This is such a basic safety feature of communications that I can’t imagine you really are being serious about what you’ve written. Where you really have to be behind is when using CPDLC clearances for level changes. Sometimes it may happen that the crew pressed WILCO and started the climb as instructed but we didnt receive the answer. ATC has to assure they are following the clearance eg“DLH123 I did not receive CPDLC response climb FL360”; voice readback req!

@pcfreakxx I an referring to cases where compliance would be immediately evident.  "Change squawk to 5753” radar scope shows new squawk of 5753 I acknowledge the value of recording it on ATC tapes.  In the railroad biz there's a whole science to when messages must be acknowledged vs when they do not.


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What does "short parked" mean?
Recently, when flying (as a passenger of a regular flight) from Stockholm/Arlanda, there was quite a long bus ride from the gate to the aircraft, because the latter was "short parked", according to the announcements at the gate. What does "short parked" mean? "Faraway parked" would have made more sense from a passenger point of view.

I don't think it's an official term, but it's possible the reference point is the aircraft, not the terminal. "short parked" might mean the aircraft parked in a remote stand in order to have a short taxi

"short parking" seems to be an informal European term for "short-term parking".  So it's referring to the time a vehicle is parked, not the distance.
If I heard it about the location of an airliner, I'd think they meant that the gate areas were full and it had to be put somewhere temporary (and inconvenient) this time.

The term is rarely used, at least that I am familiar with in the US, but the times I have heard it used, the aircraft is parked on a ramp, away from the terminal building.  This has always been close to a main taxiway, and away from the pushoff movement area around the terminal building.
The line crew have called it short parked, because the taxi is substantially reduced.  The aircraft might be 3000 feet from the terminal building.
This has been observed more frequently with charter and special flights, even though the carriers are normal 121 operators.  Sometimes the aircraft parked in this area are military transports which are too large or too heavy for the FBO ramps.


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Why is the circulation around a centrifugal impeller blade tip the opposite to a wing tip?
Why does the circulation around a centrifugal pump blade tip go from low pressure to high pressure as an effect of the slip caused by the non-uniform velocity distribution (the opposite of a wing tip). The reason stated in my book says that below the blade there is low pressure leading to high velocity and vice versa for the part above the blade. In an airplane, there is vortex at wing ends where air moves from below(high pressure) to above(low pressure) as given in the diagram.

Also how less pressure leads to high velocity? Don't tell me to use bernoulli as the flow has vorticity.

Deepak, your second picture depicts wing tip circulation, which may be a different consideration from evaluation of 2D "circulation" of an airfoil.

I think what's confusing you is that the text book is using the term circulation to describe speed relative to the average airflow, not actual circulation around the blade.
There's still a black arrow pointing outwards on the high pressure side of the blade - no air is travelling inwards.
However if you look at the difference between actual speed and the average speed, it's negative on the high pressure side and positive on the low pressure side.
I don't fully understand the theory, but I think you're supposed to imagine the surface of the aerofoil (or an infinitely thin layer of air next to it) to be circulating, and causing the velocity gradients.
Wikipedia says:
Circulation is often used in computational fluid dynamics as an intermediate variable to calculate forces on an airfoil or other body.

I think you do understand it fairly well.  Look a nor'easter compared with a hurricane.  The circulation in a hurricane is perfectly circular.  The faster moving nor'easter has air flowing "up" and over the "top" of it, and a "downwash" behind it.

It is important to visualize the flow into this pump is on an axis perpendicular to the plane of the diagram, flowing towards it.  The pump spins "clockwise", there for higher pressure will be on the right side of the blades.
But the centrifugal pump, true to its name, adds energy to the fluid by its rotation, which slings the fluid to the right.  The "centrifugal force", really the fluid being propelled to the right 90 degrees from its in flow, drives it at much higher velocity towards the outside of the impeller.
The circulation circled in the diagram seems to be a minor part of the total flow.  Though there may be some, the majority of the inflow will be driven towards the outside of the impeller as new fluid is drawn in.
Centrifugal compressor designs are seen in early jets, and are still seen in R/C model jets.
Upon futher inspection, look closely, the circulation is the SAME as a wing.  Because the wing is in motion, the circulation may not be fully closed, but the lower pressure areas created by the airfoil as it passes through the air imparts energy to the air in a similar manner as the pump (top lift), as well as the higher pressure area underneath the wing (bottom lift).
The impeller blades are curved oppositely as what we may expect to see in a "wing". Keep in mind this is a rotating device.  The outer part of the impeller blade moves much faster.


text:
Is failure to comply with evacuation procedures illegal?
In every flight, we are instructed that we must leave our personal belongings in case of evacuation. I remember also notified that it is illegal not to follow the rules (I don't remember if this goes only for the non-smoking rule though).
So, is it "illegal" to take your stuff with you, while instructed to leave the airplane in an emergency (thus stalling the process)?

@ymb1 so the answer is yes? BTW, I don't see the reason for downvote and close vote, and more importantly I don't see guidance/explanation for those.. I remember this place was once very helpful. :/

Well, it's obviously not "OK" so the title might have struck some as attention-getting and self-explanatory, perhaps.

@quietflyer hmm can you please suggest how to improve my question? The way this site evolved makes me afraid of posting a new question, every time.. :/

Well I was just talking about the title specifically.  Maybe change "ok" to "legal" if that's still within the meaning you intend.  I didn't downvote though

If you watch video of runway evacuations you'll see a lot of passengers from any and all doors carrying their carryon stuff. It's not just Business class; it's everyone.

Btw was the aircraft in fact on fire before landing?  Not saying it wasn't, just haven't followed closely. Not to speculate about cause of crash but if that is not known factual info then it might be a reason for downvote of question and certainly would be a reason to modify question

Simon I am talking about business class on this specific incident. I saw a video of people videotaping the fire from inside, while seated. Surely that wasn't while the evacuation was ongoing.

@quietflyer "was the aircraft in fact on fire before landing?" Looks doubtful. See e.g. BBC's Aeroflot plane crash: Pilot error theory probed from May 7, where there's a second-hand quote indicating that the fire began after touchdown. That said, it is of course possible that the pilots didn't realize the airplane actually was on fire.

"is it legal?" in this case would probably mean "is it legal according to Russian law?". I hope we have a Russian aviation legal expert around...

@aCVn good point. That accident was just the cause of my question. My intend though is more on the places I am going to, like EU and USA, so question edited, thanks!

No. The intent of the statute involves "assaulting or intimidating" a crew member. Passively failing to obey a crew member has no criminal liability nor does disobeying generic safety guidance given by crew members or aircraft literature.
The actual statute reads like this (49 U.S.C. § 46504):

An individual on an aircraft in the special aircraft jurisdiction of
  the United States who, by assaulting or intimidating a flight crew
  member or flight attendant of the aircraft, interferes with the
  performance of the duties of the member or attendant or lessens the
  ability of the member or attendant to perform those duties, or
  attempts or conspires to do such an act, shall be fined under title
  18, imprisoned for not more than 20 years, or both.

Normally, disobeying a crew member generally has the effect of getting the passenger kicked off the flight. Note that a captain can remove any person for ANY reason from a flight, nor does the captain need to give a reason. Of course, if the flight is in progress, then removal is not an option.
(Also, note that this answer is for the United States only. In authoritarian/Salic law type places like France or Germany, they have laws that generally make it criminal to disobey authorities, which is different than the United States.)

"Of course, if the flight is in progress, then removal is not an option." -- well not a legal or advisable one, anyway.

It is not generally a criminal offence to disobey an authority in Germany. It is however a crime to cause other people harm or death due to gross negligence (see here or here e.g.).

It might be worth noting that this might change after the Moscow accident where one of the passengers caused a bunch of people to die by blocking the evacuation by getting his bags.

The part in parenthesis is a weird take considering that in the USA police routinely shoots people on the spot for disobeying authorities.


text:
How do pilots decide whether or not to deploy a ram air turbine?
Since the turbine needs to be deployed from within the aircraft to the outside, it will obviously induce aerodynamic drag (slowing the plane down?).
I mean I remember reading an article where a plane that for whatever reason did not stow it's landing gear and ending it burning significantly more fuel than planned.
So my question is what checklists and other factors to pilots need to account for before they decide to deploy the RAT

It is usually deployed automatically when power systems fail. I can't think of a reason a pilot would deploy the RAT unless they needed power (all engines-out).

If you tell this to an engineer their answer is probably "why would you want to do it?" "Really? Computer X and subsystem Y is simply not designed to handle power loss." "Do you have any idea how much damage controller Z can do when it's losing power but not complete incapacitated yet?" "I don't know, for your safety we just make very sure RAT is deployed before that".

Inflight test for maintenance is a good reason (needed on some airplanes). The question can be better put as "when somebody accidentally hits the wrong button and deploys the RAT, do you need to divert?"

The reason why the RAT deployed is of primary concern. The RAT should automatically deploy when (depending on the design of the aircraft) you lose all primary electrical and/or hydraulic power. In these cases, an immediate diversion is necessary because you may be one failure away from losing control of the airplane.
However there are uncommanded RAT deployments due to system malfunction, or mistake. For example, the pilot hit the RAT button by accident, or somebody accidentally switched off both generators instead of switching on both bleeds. In that case, the problem is easily rectified and then the pilot needs to decide whether to divert/return or continue the flight.
For Airbus, they state

The uncommanded extension of the RAT is not considered to have any additional operational impact. The RAT is able to be extended in all flight envelope conditions. If there is an uncommanded RAT extension, then this is indicated to the flight crew, and hence the appropriate maintenance action, i.e. the resetting of the RAT, can be performed.

Fuel burn is minor, I think its +1% on the A320 family. The main concern operationally is that a RAT is loud. They sound like a prop plane or helicopter, so for passenger concerns, you might end up landing and having it restowed.

So it seems like the RATs used in commercial aviation have no way to be restowed without assistance from the ground?

@Ksery Correct. Basically the propeller only fits in the aircraft in a certain orientation, so somebody has to align it on the ground.


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What is this on top of the Air Force One?
Clarification: It wasn't Air Force One that visited Switzerland, it was the 747-200 E4 carrying Ashton Carter. Source
What is this thing on top of the plane (In red circle):

On other "Air Force One" Google image searches, I can't find this thing. I know they have more than one 'doomsday-plane', but whats the purpose / use of this thing?

The aircraft is the Boeing E-4B Advanced Airborne Command Post 'Nightwatch', which serves as the survivable mobile command post for the US National Command Authority. The aircraft are based on the same Boeing 747s as the VC-25s used by US President.
There are four identical aircraft performing this function in the US. The "bulge" on the top is a radome that houses a steerable SHF SATCOM antenna, as can be seen in the following image.

Image from cnet.com
The following image shows the aircraft systems in a little more detail.

Image from http://everythingisahoax.tumblr.com
As a side note, Air Force One refers specifically to USAF aircraft carrying the US President. From US DoT ORDER
JO 7110.65W

When the President is aboard a military aircraft, state the name of the military service, followed by the word "One".
EXAMPLE−
“Air Force One.”
“Army One.”
“Marine One.”

For civil aircraft, it is Executive One.

And - a bit OT - if the President is on a naval vessel (eg. a submarine or a carrier), it should get the call-sign "Navy One" for the duration.

So, translating from milspeak, it houses a directional microwave antenna for satellite communication, amirite?

Marine One happens reasonably often — it seems that generally when the president is on a helicopter it's provided by the Marines.

@BaardKopperud George W.Bush flew a naval aircrafl (S-3B Viking) while being President. it was called Navy One.

@BaardKopperud Just to hone my nitpicking skills, George W Bush did not fly the S-3B, he was a passenger.

I do wonder as an aside how long that VLF antenna spools out too. And I am guessing it’s a receiver only?

Well, one of the E-4s could be Air Force One, iff the president happened to be onboard for some reason.

@jCisco The trailing wire antenna is 5 miles/8 km long. It is capable of transmitting and receiving VLF communications with submarines. The length deployed at any given time is adjusted to tune the antenna to the frequency in use.

That is not simply an E4, but a "B" variant.
The hump houses a SHF antenna. (Source)

December 1979 a fourth aircraft (75-0125) was added. This aircraft was fitted with the distinctive “Hump” on the back of the upper deck, housing the SHF antenna. It also offered upgraded accommodations, additional shielding, upgraded electronics and new CF-6-50E2 engines. This became known as the E-4B model.


text:
What is the weather term for snow and dust mixture?
An old pilot friend of mine told me today a story that I thought was interesting.
He said that he was flying into Wichita, KS a couple decades ago and was listening to the ATIS when the weather report indicated snerd.  He called up the approach controller and asked what snerd was and the controller stated it was a mixture of the blowing snow and dust coalescing making a big mess.  The pilot stated he broke out of the clouds and all he saw was a brown mess all over the place.
Does anyone know if this is actually called snerd? If not, what is the correct term?

Current METAR coding would break down the phenomenon to its basic elements and describe each discretely, for example: BLSN DU (blowing snow, dust).

I lived and flew in North Dakota for about three years. While I was there, people talked about (and I experienced) the delightful mixture of snow and dirt called snirt. It can be the result of plowing sanded roads, and also can be caused by the high winds that come out of Canada blowing dirt from fields onto areas still covered in snow. Google image search has some good examples.
I have a feeling that's what was described by your friend. It appears in Wikipedia's list of types of snow, but as far as I am aware it is not an FAA or NOAA term.

I've never heard of that, as an aviation term or otherwise. The term doesn't show up on the NOAA page for decoding METAR reports, and a Google search doesn't show anything promising along those lines either.
I think the most informative part of the annecdote was that it was from a few decades ago -- weather reporting wasn't quite as standardized then as it is now, and local terms probably got more use then.


text:
What is block hour in ACMI lease?
What is difference between Block hour and Flight Hour?
In ACMI Lease of aircraft, prices are calculated based on block hours. What is a block hour and how are they calculated?
Can any one show me an example for a flight like this...

Delay at Runway (takeoff): 20 Minutes
Flight Time: 1 Hour and 40 Minutes

Then what could be block hours? 2 Hours or 1 Hour and 40 Minutes?

Block time starts when the aircraft is pushed back from the gate, and ends when it arrives at the corresponding gate.
It is the total time the aircraft is in use, typically only calculated for revenue movements.
Imagine a flight:

Pushback 1000
Taxi 1030
Takeoff 1035
Touchdown at destination airport 1445
Taxi to gate 1500

Total block time is 5 hours

Dear, can you please tell me what is Taxi time and pushback for an aircraft?

Pushback is when the airplane is literally pushed back from the gate, normally with a tug. It is moved to a designated area where the pilots turn on the engines and then start taxiing under their own power. Taxi time is quite literally, the time spent taxiing the aircraft - normally calculated from the time the aircraft exits the active runway and ends when the aircraft arrives at the gate and the parking brakes are set (for arrivals), and the time the aircraft moves under its own power (for departures) to reach the active runway. The time spent on the active runway is not counted as taxi time

Thanks, it is really informative, can you also tell me what is Route Navigation Facility Charges? and how it is calculated?

You should ask a new question, as the comments are not for discussions.

As I am new, I have to wait for 2 days to ask new question, no worries, but thanks again

RNFC is an umbrella term which covers all kinds of flight charges (for example, landing and take off fees, parking fees, overpass fees) and differ from place to place. They would depend on your equipment type and what route you are flying, and what kind of services you would need if you stop (for example, technical stop fees are different than deplaning).


text:
Where does the water salute come from?
Water salutes by the fire crew are regulary done for certain events like plane retiring, or an new airplane delivered and much more. But where does it come from? And why should the fire service do a water salute even if they don't really care about a pilot retiring?

This may come from fire boats doing the water salute in harbors.

What else does the fire service have to do? They're obviously not going to do it if they would otherwise be occupied with an emergency, so the fact that they're doing it means they aren't busy. Spraying some water around is probably at least as interesting an activity as doing training or maintenance or playing cards, so why not?

Here is a report on the tradition of the water salute. The tradition does really come from the Marine world, but I'm not sure there is a pin-point of the first use of it for aviation purposes.

@RonBeyer - that looks like an answer to me! There wasn't a question about "first use", so addressing the tradition seems to fulfill the need.

Nasa started to spray (serious quantities of) water to celebrate rocket launches.

Water salutes are purely ceremonial and have no practical value. There are no confirmed reports on when it started in aviation, but it became common in the 1990's.
Before aviation, this practice started for ships on their inaugural voyages or returning from a long voyage. At New York harbor, jets of water were sprayed from fire boats.
Commonly, water salutes are done for:

first flight of an airplane
first or last revenue flight of an airplane
last flight of a retiring pilot
carrying a fallen soldier

Mostly, it attracts attention and looks cool without costing a huge amount or having anything to clean up.

Fire Services usually test their equipment weekly. If you give them some notice they will schedule that weeks test to accommodate a special event.
I've seen them hose down the area next to the fire station to please a school trip so I bet its not an issue for them.

That's interesting, do you have some document to support this claim and make it factual?

A water salute is a bit more formal than just having fun spraying down a sidewalk. It's usually at an event, and showcases a ceremony of sorts.


text:
Would injecting water into a jet engine’s exhaust increase velocity?
Can high pressure mist of water be sprayed into jet engine exhaust, to create steam, to increase velocity? Would the steam generated from high pressure water being injected into the jet engine exhaust increase velocity?

Related: https://aviation.stackexchange.com/questions/36185/how-does-jet-engine-water-injection-work and https://aviation.stackexchange.com/questions/33482/why-is-water-contaminated-fuel-bad-but-water-injection-is-not

Not a duplicate, at least as I read it. Normal water injection is injecting water into the air before (or as) combustion takes place. This is talking about injecting water into the exhaust (i.e., post-combustion).

Well, where does the energy of the "high pressure" water come from?

This problem can be modeled as: for a fixed volume and mass of high pressure hot gas, how much water can you inject into it while the pressure increases or remain the same.

@kevin: Presumably, a pump driven by the engine itself. But the extra thrust isn't provided by pumping out liquid water; the obvious idea is that this water vaporises and thereby turns exhaust heat into useful, kinetic energy. Not a bad idea; heating the sky is a form of energy loss.

If given the choice of carrying gallons of water, or extra gallons of fuel, more fuel would always be the better choice.  Even if water/steam can create thrust, an equal amount of fuel would create more thrust.

Not a duplicate, at least as I read it. Normal water injection is injecting water into the air before (or as) combustion takes place. This is talking about injecting water into the exhaust (i.e., post-combustion).

Spraying water into the exhaust stream will cool down the exhaust flow. The energy needed to heat and evaporate the water needs to come from somewhere, after all. The cooler and denser exhaust flow will slow down, so its impulse will become lower, reducing thrust. While the mass flow will go up, its speed will be reduced. Since water enters the flow as a liquid and leaves the nozzle as a gas, its evaporation enthalpy is irretrievably lost and removes energy from the exhaust stream. The slightly higher mass flow in combination with a lower speed will result in a lower impulse.
If you spray water into the intake flow (or after the first few compressor stages), the same evaporation enthalpy will allow a higher mass flow in the intake, so a higher mass flow in the combustion chamber can be achieved. Also, the cooling of the intake air allows to add more fuel in the combustion process, so more thrust can be created. Of course, this is bought with higher fuel flow.

The first steam engines like the Newcomen Engine used water injected into the cylinder filled with steam in order to condense the steam in cylinder pulling the cylinder down. This is just a practical example of what water injection into the exhaust would do. Plus the aircraft would need to carry a large water store in addition to fuel reducing available pay load.

The cooler and denser exhaust flow will now also contain evaporated water mass. Thrust is created by the exhaust mass flow times velocity.

@Koyovis: Yes, but in order to contribute impulse, the water mass also needs to be accelerated. In addition to absorbing heat, it will steal impulse from the exhaust flow in order to speed up. This reduces the impulse of the exhaust flow (minus water) even more. The secret of water injection is to allow more fuel. Only this additional fuel creates more thrust.

?? The steam doesn't expand when it evaporates? A steam turbine does not provide thrust when the turbine is removed?

@Koyovis: Yes, the steam expands. But since overall the temperature decreases, this does not compensate for the increased density. How else should proper water injection work? The physics is the same, regardless where the water is injected.

Um - that's my point as well.

@Koyovis The steam expands, but is an endothermic process, so it absorbs energy in doing so. It would be an overall energy reduction. The steam turbine works because the steam is heated in an enclosed chamber before being sent through the turbine. It absorbs energy in a boiler and releases energy by cooling and condensing as it passes through the turbine. The exact opposite of what it would do in jet exhaust.

@TomMcW Not so, my friend. Drip cold water on a hot plate, and steam escapes that could drive an old steam whistle: thrust. Combined cycle power stations use a gas turbine, plus a steam turbine using the waste heat from the hot exhaust of the gas turbine. Heat is energy already, wasted energy when it leaves the jet exhaust. Inject water into it, and the phase transition from water to steam converts some of this energy into impulse.

@Koyovis: No, please no apple to orange comparison. A stationary turbine cannot use its exhaust impulse, so it makes sense to add something that extracts mechanical energy from it. An airplane engine needs that impulse for thrust; reduce it and thrust is reduced.

@PeterKämpf Does the steam expand more than the main exhaust stream contracts, is the question. I say it does. but I cannot quantify it. Can you?

@TomMcW Just did a back-of-the envelope calculation and it looks like you and Peter are correct, the exhaust air stream contracts more than that the steam expands. I'll check again tomorrow morning & edit the answer.

@Koyovis I'd be surprised if it didn't. Just from a conservation of energy pov the endothermic process has to remove energy, either from pressure or velocity. Once again, the combined cycle generator is heating water in an enclosed boiler, so the dynamics won't be the same.

@yshavit: Thank you, corrected. Of course you are right.

@TomMcW Surely from a conservation of energy viewpoint, the combined energy of the exhaust stream and water mist must remain more or less constant (assuming that little is gained from or lost to the surroundings, which I think is safe over short timescales). Any energy lost from the exhaust gases is gained by the water, so it's purely a question of whether the gas contraction is outweighed by the water-to-steam expansion. It's also worth noting that the water mist would cool the exhaust nozzle, using energy that might be otherwise lost.

@anaximander That is my point exactly. The engine creates energy by burning fuel. Then after that you add cold water. The water is not going to add any energy to the mix, it will only absorb energy through the process of heating and changing state. There's a reason we spray water on a fire, to remove energy. There's just no way that spraying water into the exhaust could add anything to it. It would be neutral at best.

@TomMcW You're missing that the water becomes part of the system. When we spray water on a fire, it cools the burning material and that's all that matters; we don't care where the water goes. When you spray water into a jet exhaust nozzle, it removes energy from the combustion product gases, but that energy is added to the steam, which is still coming out of the back of your jet engine. You can't disregard all the energy in the steam as "lost". One unit of water expands ~1600 times when it becomes steam, so it's entirely possible that the resultant pressure in the nozzle is actually higher.

@anaximander: Like pouring water on an oil fire?

@anaximander: You totally forget the phase transition. Air enters and leaves the engine as a gas, but the evaporation enthalpy of the water really is lost and will not magically help to increase thrust.

Water injection in the exhaust could work if:

The water is fully evaporated before it exits the engine exhaust. The fuel injected in the combustion chamber must also be fully evaporated for effective combustion, and this does take some time end effort - and temperatures in the combustor are higher than in the exhaust.
The injected steam counteracts the effect of the exhaust jet contracting due to extraction of heat to vaporise the water (it does not seem to, see edit below).

Older type military jets used to use water injection back in the days when jet engines were narrow, noisy pipes. Not really required anymore since high bypass ratio turbofans were invented: almost all energy in the hot flow is used for driving the fan blade and the bypass air. Injecting water mist in the engine could still convert some waste heat into free thrust - free if we're not considering the extra infrastructure, tanks, piping etc.
Re-using exhaust waste heat is an old idea first applied with the turbo-charger, patented by Alfred Büchi in 1905. In power stations, this principle is used in combined-cycle power plants to increase overall efficiency:

A combined-cycle power plant uses both a gas and a steam turbine together to produce up to 50 percent more electricity from the same fuel than a traditional simple-cycle plant. The waste heat from the gas turbine is routed to the nearby steam turbine, which generates extra power.

A steam turbine extracts rotational energy from the hot gas turbine exhaust flow. This works for combined-cycle power plants because of the dynamics of the heat transfer, injecting water directly into a gas turbine exhaust does not do much for thrust. There are better ideas:

Inject water in the compressor, which cools down the flow and increases air density. Since the internal volume of the engine is fixed, increased density means a higher air mass flow through the engine. The science behind this is further explained in this NACA document of 1947. It mentions water/air ratios of 0.05, resulting in a further 5% increase in the total mass flow.
Inject fuel in the exhaust stream! In the old turbojets there was still a lot of oxygen in the exhaust stream, combined with the high temperatures this gives afterburner thrust.
Use a bypass fan and extract more energy from the exhaust for the turbine that drives the fan.

Edit
Steam expands, but cooler exhaust gas contracts. Injecting the water increases the mass flow with the water weight. Is the total effect beneficial? By means of a back-of-the-envelope check, we could consider a volume of exhaust gas at high temperature, and check how the volume changes after injecting water to create steam.
If we take 10 m$^3$ exhaust gas (air) at 1000K, and inject an amount of water m$_w$ in it so that temperature lowers to 800K, the exhaust gas will contract. How much water do we inject, and does the resulting superheated steam have a higher volume than the contraction due to temperature? All at constant pressure of 100 kPa.

10 m$^3$ exhaust gas (air) at 1000K weighs 3.8 kg (source)
at 1000K, C$_p$ of air is 1.14 kJ/kg.K (source)
in order to bring 3.8 kg air from 1000 to 800 K, we need to extract $1.14 \cdot 200 \cdot 3.8 $ = 866 kJ
to transform 1 kg water @ 300 K to Steam @ 800 K, we need 3444 kJ: C$_p$ of water, enthalpy of phase transition water -> vapour, C$_p$ of steam (source).
so we need to inject 866/3444 = 0.25 kg of water.

The exhaust air has reduced in volume: 3.8 kg air @ 800K is 8.26 $m^3$, so it has lost 1.74 $m^3$ from density increase.
1 kg superheated steam at 800K has a volume of 3.5 m$^3$ (source), so 0.25 kg takes 0.25 $\cdot$ 3.5 = 0.88 m$^3$.
Conclusions:

Exhaust volume has reduced from 10 to (8.26 + 0.88) = 9.14 m$^3$ = 8.6%.
Mass has increased from 3.8 kg to (3.8 + 0.25) = 4.05 kg = 6.6%

Because of the decrease in total volume, jet exhaust velocity will be lower. Thrust is mass flow * exhaust velocity - the increase in mass flow does not compensate for the decrease in velocity.

The better answer IMO. My summary: turbines driving bypass fans are simply more efficient in turning heat into thrust.


text:
What are the crewing requirements for a B787 flying LAX to SIN?
I’m wondering what the crew size, and rest requirements for the flight crew of a Boeing 787-9 flying LAX to SIN (Flight number UA37).

To save you the Google, it's an LAX-SIN flight on a Boeing 787-9 with flight times of around 17 and a half hours.

Welcome to Aviation.SE, may I invite you to take the tour and read the [help] so you can get to known the site? You're original question is likely to be closed as too broad or off topic as different air craft could be used for that flight, I will suggest an edit which I think will improve the question. You can also edit the question to improve it after.

@downvoters yes this isn't a perfect first question but this is a new user, do you think we could try helping them rather than penalising them for being new and not knowing the site?

I can't provide a specific answer but rest times are contract matter and airline specific. Also, most curiously, you won't find rest crews on private jets.
Depending on the airline you will have anything between 3 and 5 pilots on longer flights (anything above 8h). Three being the most common. Start and landing are handled by captain and co pilot, in between the aircraft is flown by a "cruise pilot" of a lower rank.
Rest crew regulations can cause problems, if there is a delay. Even a small delay may cause to require a standby crew, which will incur a further delay.
As a rule of thumb, airlines have around 10 flight crews per aircraft to allow for relief crews, training, holidays, ...